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Hermit Crab Homes

Hermit crabs do not need to worry about the rising price of real estate on the Vineyard.

It is not that they are in the lottery for an affordable homesite, nor will they inherit a house from a wealthy relative (although they might steal one.) Home ownership is just not a priority for this creature. It has no desire to settle down permanently; its affinity for moving makes it destined to be a renter, but never an owner.

Easy to find and handle, hermit crabs are by far one of the most delightful crabs around, even if they are more closely related to shrimp and lobsters than to true crabs. True crabs have a full exoskeleton or shell for protection, but the hermit crab has only a half-shell on the front part of its body. Protection is provided by another’s shell that the hermit crab has found on the sea or pond bottom.

Snail shells are the preferred residence for these crabs. The larger variety, the flat-clawed hermit crab, will commandeer a moon snail or other type of medium-sized shell, while the smaller of the two species found here prefers periwinkle, slipper, or oyster drill snail shells. Hermit crabs are well adapted for their domicile. The tail end of the animal is soft and its abdomen ends in a hook, called a uropod, that winds around the central spire (columella) of its protective shell.

Don’t try to pull the hermit crab out: it will certainly harm and probably kill the animal by breaking it in two. This crab will leave the safety of its shell only for reproduction or to find a larger shell.

The housing problem begins when the crab grows. Although the hermit crab does molt and grows another chitinous exoskeleton as it increases in size, its borrowed shell will not get bigger. It must find a new larger one.

Hermit crabs are somewhat particular and will try on a few for size. If their dream home is already occupied by another hermit crab, they will challenge it and try to win the sought-after locale by force. It could be called a hermit crab’s version of musical shells.

While demanding its own shell, the hermit crab, regardless of its name, does not like to be alone. Its shell becomes a condo of sorts, providing homes to other hangers-on, including slipper snails and barnacles.

Perhaps the most interesting housemate of the hermit crab is the colonial hydroid called snail fur. Snail fur is the aptly named fuzzy covering on some hermit crab shells. This fuzz is actually an animal, or more accurately a colony of animals.

A colony of hydroids has three types of individual polyps that feed, reproduce, or provide defense for the group. In a mutualistic (benefits both) relationship, the hermit crab has an added layer of defense and the snail fur gets access to more food as a hitchhiker on the moveable shell.

While the Island summer shuffle is notorious, the hermit crab plays its own shell game — and prospers. In the end, it doesn’t matter where the hermit crab lays it head. For this animal, home will always be where the heart is.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.